I ended up buying a Synology NAS (which does offer the same computer backup features + revisioning and all that), and then syncing the backup out to B2. It's not an ideal solution by any means, and I would get rid of my NAS in a heartbeat if there were a real solution for Linux desktops.
It really sucks to have had to go through all of that setup (+ have another machine to maintain) when I just wanted to get things done and know my data was safe.
Would you consider working with the community to find a better solution? Maybe offer a closed source library (a la libspotify, but for Backblaze) for the storage bits + get the community pointed in the right direction for an open source frontend for Linux or something?